Flame-retardant for engineering thermoplastic applications

ABSTRACT

This invention provides a flame retardant for polymeric compositions which is a mixture consisting of high molecular weight brominated epoxides modified with tribromophenol, having a low content of organic solvents. The invention further relates to a method for the preparation of the retardant, and to its use in flame retarded engineering thermoplastics having good chemical, thermal, and mechanical properties.

FIELD OF THE INVENTION

This invention relates to flame-retardant high molecular weightbrominated epoxides modified with tribromophenol, and their applicationin engineering thermoplastics, resulting in thermoplastic compositionsthat are thermally stable and have high impact resistance, high meltflow index and low melt viscosity.

BACKGROUND OF THE INVENTION

The high molecular weight (HMW) brominated epoxides (BE) to which theinvention refers have the general formula (I)

wherein n is an integer.

They are end-capped by glycidyl groups. This invention is concerned withHMW BEs modified with tribromophenol (TBP). If both of the end glycidylgroups are substituted by tribromophenyl-oxo-2-hydroxypropyl groups, theresulting compounds are phenoxy compounds which have the general formula(II)

wherein n is an integer.

However, it may be that only one of the end groups is substituted,resulting in compounds having the general formula (III)

wherein n is an integer.

Mixtures of compounds of formula (I) and/or (II) and/or (III), whereinat least 80 mol % of the end groups aretribromophenyl-oxo-2-hydroxypropyl groups and at most 20 mol % of theend groups are glycidyl groups, will be called herein “fully modified”or “fully end-capped” (HMW MBEs).

Brominated epoxides, unmodified or partly or fully modified withtribromophenol are known in the art. Japanese Laid-open PatentPublication 1-287132 discloses styrene compositions comprisinghalogenated compounds having epoxy groups at both ends. JapaneseLaid-open Patent Publication 5-117463 discloses styrene compositionscomprising halogenated epoxides. Japanese Laid-open Patent Publications62-4737 and 63-73749 disclose a fire-retardant mixture comprising morethan 60% of halogenated epoxy fully modified with TBP. JapaneseLaid-open Patent Publication 1-170630 discloses using as fire retardantcompound a low molecular weight brominated compound 50% end-capped withTBP. All the above compositions are defective in light resistance, heatstability or other properties. U.S. Pat. No. 5,837,799 proposes as afire retardant compound a mixture of HMW BE unmodified, modified at oneend with tribromophenol, and fully modified (20 to 35 mol % is fullycapped with tribromophenol). This mixture however is defective in thatit will cause gel formation (by cross-linking) when processed withengineering thermoplastics such as polyamides, thus impairing theprocessing steps.

Low Molecular Weight (LMW) BEs have low viscosity and therefore it isrelatively easy to reduce the volatile content to very low levels byusing equipment which is known to those skilled in the art. On the otherhand, HMW MBEs are very viscous, even at higher temperatures, and it istherefore very difficult to reduce the volatile content to very lowlevels. It is therefore advantageous to use LMW BEs with very lowvolatile content as a starting material for the production of HMW MBEs.Japanese Laid-open Patent Publication 2001-310990 discloses BE which maybe fully modified with TBP and discloses a method that requires the useof solvents in the polymerization stage to produce HMW MBEs. Thecompositions obtained according to its teachings are defective becausethe flame retardant is prepared in an organic solvent and thereforenecessarily contains a significant amount of organic volatiles. Thesevolatiles cause metal corrosion and failure of metallic parts which arenear to or in close contact with the flame-retarded engineeringthermoplastics.

It is therefore a purpose of this invention to provide flame retardantand flame-retarded compositions, which are free from the defects of theprior art.

It is another purpose to provide flame-retarded engineeringthermoplastic compositions which have high impact resistance.

It is a further purpose to provide flame-retarded engineeringthermoplastic compositions which have high melt flow index and low meltviscosity and maintain these properties under long residence time athigh processing temperatures.

It is a further purpose to provide flame-retarded engineeringthermoplastic compositions which minimize corrosion of metallic partsthat are near to or in close contact with the thermoplastics.

SUMMARY OF THE INVENTION

The invention provides a flame retardant which comprises fully modifiedBEs, viz. a mixture of compounds of formula (I) and/or (II) and/or (III)in which at least 80 mol %, preferably from 85 to 100 mol %, of the endgroups are tribromophenyl-oxo-2-hydroxypropyl groups and at most 20 mol%, preferably from 0 to 15 mol % of the end groups are glycidyl groups.The flame retardants of the invention additionally have the followingcharacteristics:

-   -   high molecular weight (between 7,000 and        50,000—Dalton—preferably more than 7,000 and less than 30,000);    -   free tribromophenol content less than 0.1 wt % of the whole        flame retardant;    -   organic solvents, with boiling point lower than 250° C., less        than 100 ppm, and preferably less than 50 ppm, of the whole        flame retardant.

The said flame retardants also have preferably an acid number less than1 mg KOH/g and preferably less than 0.5 mg KOH/g of the whole flameretardant and an epoxy equivalent more than 10,000.

The high molecular weight BEs of the invention fully modified bytribromophenol will be briefly indicated hereinafter by the initial HMWMBE.

In a preferred embodiment of the invention, the HMW MBE comprise from 70to 100 mol % of modified BEs of formula (II), from 30 to 0 mol % ofpartly modified BEs of formula (III), and from 10 to 0 mol % ofunmodified BEs of formula (I).

Another aspect of the invention is a method for preparation the HMWMBEs. Said method comprises the steps of reacting low molecular weightbrominated epoxide (LMW BE), having low volatile content, withtetrabromobisphenol-A (TBBA) and tribromophenol (TBP) in the presence ofa catalyst. The molecular weight of the LMW BEs is between 650 and 3,500Dalton. The reaction takes place without any solvent at a temperature of100 to 250° C., preferably 100 to 200° C. TBP can be replaced totally orpartly by tribromophenylglycidyl ether.

Another aspect of the invention are polymeric compositions comprising abase polymer chosen from among polyesters, such as but not limited topolyethylene terephthalate or polybutylene terephthalate, or mixturesthereof, or polyamides or polycarbonate and its alloys, and comprisingthe HMW MBEs of the invention.

A further aspect of the invention is a polymeric composition that alsocontains hindered phenol antioxidant.

Said polymeric compositions may also comprise fillers and/or glassreinforcement and/or antioxidants and/or lubricants and/or pigmentsand/or antidripping agents such as polytetrafluoroethylene-based systemsand/or grades of talc that act as nucleating agents and that reduce theinjection molding cycle time.

The polymeric compositions of the invention have a higher melt flowindex and a lower melt viscosity, even under long residence time at highprocessing temperatures, than compositions containing comparableunmodified BEs. This property is particularly important in theproduction of objects with glass reinforced engineering plastics such asPBT, PET, or polyamides, as usually very thin walls and light weightsare targeted. The high molecular weight flame retardant also contributesto the high processing heat stability needed for these types ofproducts.

It was moreover found, on the contrary of what would have been expected,that these high molecular weight MBEs according to the invention, do notcause any decrease of the melt flow rate (MFR) while increasingresidence time at high temperature, unlike what is observed withcorresponding high molecular weight (between 7000 and 40,000 Dalton)BEs. This property is of particular interest for applications wherematerials are processed with long residence time or repeated heatingduring the complete series of processing steps, such as compounding,injection molding, and often, recycling of scraps. When high molecularweight (between 7000 and 40,000 Dalton) BEs are used, a significantincrease in melt viscosity (reduction in MFR) of the plastic compound isobserved with increasing residence time at high temperature. The reducedMFR results in serious limitations in injection molding properties; itmay become impossible to produce articles of thickness such as 0.4 to1.6 mm; it may increase injection molding cycles, increasing the cost ofproduction; and it may limit the loading in scraps coming from previousproduction as they would increase too much the viscosity of the melt.

Low molecular weight modified BEs having a low softening range areusually difficult to compound directly with a base polymer because whenthey are added in the extrusion compounding machine, at hightemperature, they start to soften and melt and consequently they stickonto the wall of the hopper, causing bridging later on, which willinterrupt good compounding conditions. To avoid this kind of problem,producers are often obliged to prepare in advance pellets of amasterbatch concentrate containing high loading of low molecular weightmodified BE, and this results in increasing cost and a detrimentaleffect on the final properties of the plastic composition. The HMW MBEsof the invention can be added directly as is, in a powder form, into theextrusion compounding machine, without causing any problem of softeningor bridging, and thereby enabling easy and constant compoundingconditions. Moreover, compounding operations of engineeringthermoplastic compositions containing low molecular weight modified BEsare very difficult as they cause overlubrication and exude out of theblend, making deposits on the screw and on the barrel of the extruder.This problem is solved by the use of HMW MBEs.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following Examples 1 and 2 describe the preparation of modified highmolecular weight brominated epoxy resins end-capped with tribromophenol.

EXAMPLE 1

This example describes the preparation of HMW MBEs, having a low contentof volatiles, according to the invention (F-3100 LG). A 1 liter glassreactor was equipped with heating mantle, thermometer, stirrer andnitrogen inlet. Into the reactor, 664 g of low molecular weightbrominated epoxy resin (LMW BE) made from tetrabromobisphenol A (TBBA)and epichlorohydrine was introduced, said resin being characterized bythe following properties:

Epoxy equivalent weight (EEW) 477 g/equivalent, and Volatile content  21ppm w/w methyl isobutyl ketone (MIBK).

The said LMW BE had the formula (I) given hereinbefore.

The air in the reactor was replaced by nitrogen and the LMW BE washeated, it melted at 80° C., and the heating was continued to 150° C.Then stirring was started and 323.6 g of TBBA, made by Bromine CompoundsLtd. and designated as FR 1524, and 0.03 g tetrabutyl phosphoniumbromide were added, followed by 52 g tribromophenol. The temperature ofthe reaction mixture was reduced to 100° C. and then rose exothermallyto 170° C. in 45 minutes. The reaction mixture was poured into analuminum tray and was placed in an oven heated to 170° C. After 6 hours,the tray was removed from the oven and allowed to cool to roomtemperature. The obtained product block was grounded and analyzed, andthe following properties were measured:

Weight average molecular weight 16050 Dalton Number average molecularweight 10100 Dalton Softening point 187° C. Volatile content (measuredby gas 13 ppm MIBK chromatography) Bromine content 53.1 wt % EEW 27000g/equivalent Acid value 0.07 mg KOH/g % epoxy end groups 18.5 mol %

EXAMPLE 2 Comparative

This example describes the preparation of HMW MBEs (F-3100 R). The sameprocedure as described in Example 1 was repeated, but using LMW BEcontaining 470 ppm residual MIBK. Grounded and analyzed, the followingproperties were measured:

Weight average molecular weight 16150 Dalton Number average molecularweight 10200 Dalton Softening point 187° C. Volatile content 290 ppmMIBK Bromine content 53.1 wt % EEW 26000 g/equivalent Acid value 0.08 mgKOH/g % epoxy end groups 19.6% mol %

As may be seen, most of the MIBK remained in the final product.

EXAMPLE 3

In this example it was attempted to remove dioxane solvent fromtribromophenol end-capped high molecular weight brominated epoxide bysubjecting it to high vacuum. Into a 1 liter flask of Rotavapor® (madeby Buchi, Switzerland), 300 g F-3100 LG prepared as in Example 1 and 100g dioxane were added. The flask was mounted on the Rotavapor® and dippedinto an oil bath at 90° C. and rotated at a speed of 40 rpm. After fivehours of heating, the temperature of the bath was raised to 170° C. forfour hours and then to 200° C. for two hours. Sample no. 1 was taken.After an additional two hours at 200° C., sample no. 2 was taken. Avacuum pump was started and the vacuum raised gradually as the resinbecame very viscous and foamed, filling the flask. After six hours thepressure in the flask was 30 mmHg; the vacuum was released, and sampleno. 3 was taken. The vacuum pump was then replaced by an oil pump andthe vacuum was raised gradually to avoid too much foaming. After 6 morehours at 200° C. and vacuum of 4 mm Hg, the final sample, no. 4, wastaken. The four samples were analyzed by gas chromograph for dioxanecontent. Results are summarized in the following table:

Sample No. 1 2 3 4 Dioxane content 74300 25600 3500 1900 (ppm)

As can be seen, even when employed lab conditions, it is difficult toremove the solvent from the high molecular weight epoxy resin.

The following Examples 4 to 8 illustrate the applications of HMW MBEs inpolymeric compositions.

EXAMPLE 4

HMW MBE prepared according to Example 1 (F-3100 LG), and characterizedby low organic volatiles, has been compared with atribromophenol-modified oligomeric brominated epoxide having an averagemolecular weight of 2000 Dalton (trade name F-3020, produced by BromineCompounds Ltd.) in glass reinforced polybutylene terephthalate (PBT).The compositions of the blends are given in Table I.

All the components of the blends have been compounded in a Berstorffco-rotating twin-screw extruder type ZR-25 with a ratio of length overdiameter of the screws equal to 32. The processing conditions are asfollows:

Processing Temperatures (° C.):

Zone Zone Zone Zone Zone 1 Zone 2 Zone 3 Zone 4 5 6 7 8 Die 180 220 240250 260 260 265 270 270 Screw rate: 230 rpm Feed rate: 10 Kg/h

The feeding was performed by a gravimetric feeding system K-SFS24 ofK-Tron. A dry blend of PBT and antimony trioxide master batchconcentrate, both in a pellet form, was fed via the pellets feeder,while the flame retardant was fed via the powder feeder. The glassfibers were introduced in the fifth section of the compounding extrudervia the lateral feeder.

Very soon after the start of the compounding operation, the compositionwith F-3020 began causing bridging of the blend in the lower part of thefeeding hopper, causing repeated interruption in the extrusion process.The replacement of F-3020 by F-3100 LG, produced according to theinvention, keeping all the other components in the composition the same,solved the problem completely, and no more bridging was observed,eliminating the previous interruptions during production of the compound(Table I).

Moreover, the compounding operation with the F-3020 composition was verydifficult, as F-3020 caused an overlubrication exuding out of the blend,making deposits on the wall of the screw and on the barrel of theextruder.

TABLE I Compositions of the blends (wt %) and their behavior. FlameFlame Retardant Retardant F-3100 LG F-3020 PBT Celanex 2500 (Ticona)52.3 52.3 Glass fiber pbt 1a 1 hr (Owens Corning) 30 30 Flame retardant13.5 13.5 Antimony trioxide master batch concentrate 42 42(M0112-Kafrit) Bridging in the feeding hopper of the None Significantcompounding equipment bridging

EXAMPLE 5

HMW MBE, prepared according to Example 1 (F-3100 LG) and characterizedby low organic volatiles, has been compared with a non-modifiedpolymeric brominated epoxide with a similar molecular weight (trade nameF-2100, produced by Bromine Compounds Ltd.) and with a non-modifiedpolymeric brominated epoxide with a significantly higher molecularweight (trade name F-2400H produced by Bromine Compounds Ltd.) in glassreinforced polybutylene terephthalate (PBT). The compositions of theblends are shown in Table II below. Compounding was made using the sameequipment under the same conditions as in Example 4. Compounded strandswere pelletized in a pelletizer 750/3, produced by Accrapak SystemsLimited.

The pellets produced by pelletizing said three compositions have beentested by measuring their melt flow index, using a Melt Flow Indexerproduced by Rosand and according to ASTM D 1238-82. It can be seen inTable II that the use of F-3100 LG, produced according to the invention,contributes to provide the glass reinforced PBT with a significantimprovement in melt flow index, compared with both F-2100 and F-2400Hthat are non-modified polymeric brominated epoxide. A high melt flowindex is an important advantage for glass reinforced PBT, as it producesthin wall parts with less weight, more complex shapes and in shortercycle times.

Another advantage which can be seen in Table II is the fact that byincreasing the residence time at the processing temperature of the meltflow indexer to 30 minutes, the melt flow index did not decrease for thecomposition containing F-3100 LG, while in the case of F-2100, animportant reduction of the melt flow index was observed. This means thatglass reinforced PBT compositions flame-retarded by F-3100 LG will keeplow viscosity properties, even after long residence times in processingequipment such as injection molding machines, or after severalprocessing steps, such as during the recycling of scraps, while in thecase of F-2100, the increase of viscosity will render the processingconditions more difficult and it will limit the possibility of recyclingof scraps.

The melt flow index of the composition containing F-2400H (molecularweight higher than the modified epoxides of the invention) is notaffected by a long residence time at high temperature. This type ofpellet, however, is very viscous and not suitable for the production ofthin wall parts with a short cycle by injection molding.

Molded samples have been prepared from the compositions by injectionmolding in an Arburg injection molding machine type Allrounder500-150-320S to measure properties. As can be seen in Table II, moldedsamples prepared from the composition according to the invention havethe good flame retardancy and thermomechanical properties usually neededfor the production of performing parts in the electronic and automotiveindustries.

TABLE II Compositions and properties of the blends. Flame retardant typeF-3100 LG F-2100 F-2400H Composition (wt %) PBT Celanex 2500 (Ticona)52.0 52.0 52.0 Glass fiber PBT 1a 1 hr (Owens 30 30 30 Corning) FlameRetardant 13.5 13.5 13.5 Antimony trioxide 4.2 4.2 4.2 Irganox B-225 0.20.2 0.2 Hostaflon TF207 (anti-dripping - 0.1 0.1 0.1 Hoechst) Melt flowindex (250° C. - 2.16 Kg): After 5 min residence time, g/10 min 33 27 19After 30 min residence time, g/10 44 24 19 min Flame retardancy, UL₄₄ atspecimen V-0 V-0 V-0 thickness of 0.8 mm: class Notched IZOD impact, J/m64 58 49 (ASTM D256) Heat distortion temperature, ° C. 202 202 201 (1820kPa) (ASTM D646-72)

EXAMPLE 6

This example illustrates another surprising effect derived from theapplication of high molecular weight tribromophenol-modified polymericbrominated epoxide prepared according to the invention as in Example 1(F-3100 LG), characterized by low organic volatiles. Said effect is theincrease of melt flow index of plastic compositions containing it,compared with non-modified polymeric brominated epoxide with similarhigh molecular weight (trade name F-2100, produced by Bromine CompoundsLtd.). This is a surprising effect, as low molecular weighttribromophenol-modified polymeric brominated epoxides (trade name F-3014and F-3020, produced by Bromine Compounds Ltd.) do not contribute to anincrease in melt flow index compared with similar low molecular weightnon-modified brominated epoxide (trade name F-2016, produced by BromineCompounds Ltd.) in plastics compositions. A comparative evaluation ofmelt indexes of plastic compositions is summarized in Table III. Thepellets used for this comparison were prepared on the same equipment asthe one used in Example 5. The increase in melt flow index properties isan interesting feature, as it allows improvement of the injectionmolding conditions of parts for the electronic and automotiveindustries.

In Table III, PBT stands for polybutylene terephthalate, and ABST foracrylonitrile-butadiene-styrene thermoplastic resin.

TABLE III Compositions and properties of the blends. Flame retardanttype F-3100LG F-2100 F-3020 F-3014 F-2016 Composition (wt %) CompositionA (based 86.5 86.5 — — — on PBT resin) Composition B (based — — 86 86 86on ABST resin) Flame retardant 13.5 13.5 14 14 14 Melt flow index*, 3327 14 15 15 g/10 min *Composition A: 250° C. - 2.16 Kg Composition B:200° C. - 5 Kg

EXAMPLE 7

High molecular weight brominated epoxide are polymeric fire retardantsrecommended for use in engineering thermoplastics, such as polybutyleneterephthalate (PBT) and polyester (PET). Such plastics have high levelsof properties. In addition to good mechanical properties, they must havesatisfactory processing characteristics and be stable during processing.HMW MBEs are preferred over non-modified brominated epoxide, as theformer significantly reduce metal adhesion properties of the compositionduring compounding. Metal adhesion causes thermal degradation ofstagnating parts sticking to the hot metallic parts of the compoundingmachine, which results in the appearance of black spots on the pellets.But still, these various types of brominated epoxides cause problems ofcorrosion of the metallic parts of the processing equipment, such as thecompounding extruder or injection molding machine, when they areprocessed at very high temperatures. HMW MBE prepared according toExample 1 (F-3100 LG) and characterized by low organic volatilessignificantly reduces the corrosion of the processing equipment.

Furthermore, such plastics need to be able to withstand conditions ofuse without losing properties or deteriorating in appearance. In manyapplications, they are required to meet stringent flame-retardancystandards, but not at the expense of their high performancecapabilities. For instance, in applications such as relays, switches,connectors and circuit breakers, high corrosion resistance may be neededduring the life cycle. Formulations based on high molecular weightbrominated epoxide and/or modified polymeric brominated epoxide do nothave sufficient corrosion resistance at high temperature of use. HMW MBEprepared according to Example 1 (F-3100 LG) and characterized by loworganic volatiles has been compared with the tribromophenol end-cappedbrominated epoxy resin of Example 2 (F-3100 R), which contains higherconcentrations of organic volatiles, and with a non-modified polymericbrominated epoxide with a similar molecular weight (trade name F-2100,produced by Bromine Compounds Ltd.) in glass reinforced polybutyleneterephthalate (PBT). The compositions of the blends are shown in TableIV. Compounding was made using the same equipment and conditions as inExample 4.

Compounded strands were pelletized in a pelletizer 750/3 produced byAccrapak Systems Limited. These pellets have been used to measurecorrosion resistance. Several methods to test corrosion of engineeringthermoplastics have been developed, the most important ones being Amptest and the one developed by Siemens. In this example, a test similarto the Siemens test was used. According to this test, four types ofmetallic coupons (brass, silver plated brass, German silver and tinbronze) were placed in a 1 liter sealed flask containing 25 g of flameretarded PBT plastics. The flask was heated to 170° C. and maintained atthis temperature in an oven for 15 days. The four metallic coupons werechecked visually and classified between 1 and 8 relative to the level ofcorrosion—8 being fully corroded. In Table IV, one can find the resultsof the corrosion test for each type of flame retarded compositionpellets.

TABLE IV Compositions and corrosion properties of blends. FlameRetardant Type F-2100 F-3100 F-3100 F-3100 LG + Ref R LG antioxidantComposition, wt % PBT (Dupont) 82 82 82.0 81.7 Brominated flameretardant 14 14 14 14 Antimony trioxide 4 4 4 4 Hindered phenolantioxidant 0.3 (Irganox 1010-Ciba Specialty) Properties Corrosion test,class 6–7 5–6 3–4 2

The results summarized in Table IV show that the use of HMW MBE preparedaccording to Example 1 (F-3100 LG) and characterized by low organicvolatiles significantly improves the corrosion resistance of the flameretarded plastic composition, compared with a product having highervolatile content (F-3100 R) and with a commercial grade of highmolecular weight polymeric brominated epoxide (F-2100). A furtherimprovement was obtained by the addition to the composition of hinderedphenol type of antioxidant such as Irganox 1010 (Ciba Specialty).

EXAMPLE 8

HMW MBEs prepared according to Example 1 (F-3100 LG) and characterizedby low organic volatiles have also the interesting property ofpermitting production of dust-free flame retardant systems that are 100%active with no need to use a polymeric carrier. Using the same equipmentas in Example 4, it has been possible to produce pellets with thecompositions described in Table V. If the flame retardant used ascarrier is a low molecular weight tribromophenol modified polymericbrominated epoxide with a molecular weight below the limit definedaccording to this invention, it is possible to produce pellets withsimilar compositions. The use of the dust-free system according to theinvention is very advantageous, as it eliminates the problem of feedingfine antimony trioxide powder and/or polytetrafluoroethylene (PTFE, usedas a powerful antidripping agent) during the compounding steps. It isbeneficial for the health of the workers. It is also advantageous inincreasing productivity of the compounding line.

TABLE V PTFE + Antimony Additive(s) Type PTFE Antimony trioxide TrioxideComposition (wt %) F-3100 LG 90 75 65 PTFE (Hostaflon 10 — 10 TF207 -Hoechst) Antimony 0 25 25 trioxide

EXAMPLE 9

This example demonstrates the use of the flame retardant of the presentinvention in polyamides. HMW MBE prepared according to example 1 (F3100LG) and characterized by low organic volatiles, has been compared withHMW polymeric brominated epoxy (trade name F2400 produced by BromineCompounds Ltd) in glass fiber reinforced polyamide 66. The compositionsof the blend are shown in Table VI below.

TABLE VI Flame retardant type Composition (wt %) F3100 LG F-2400Polyamide 66 42.6 42.6 Glass fiber 30.0 30.0 Flame retardant 21.2 21.2Antimony trioxide 4.24 4.24 Other additives 1.96 1.96

Compounding was performed using the same equipment as in example 4.Processing temperatures in the extruder were 230-285° C. Screw rate was350 rpm, feeding rate was 17 kg/hr.

Molded samples have been prepared from the compositions by injectionmolding using the same equipment as in example 5. The properties of themolded compositions are summarized in table VII.

TABLE VII Properties of FR GFR PA66 containing F-3100 & F-2400. Flameretardant type Flammability: F-3100 F-2400 Rating UL-94 at 1.6 mm V-0V-0 Rating UL-94 at 0.8 mm V-0 V-0 Comparative tracking index (V)300–325 300–325 Spiral flow* (inch) 41.2 30.0 HDT, ASTM D646 @1820 kPa(° C.) 244.1 243.3 Notched Izod Impact, ASTM D2244 (J/m) 99.4 83.3Tensile strength at yield, ASTM D638 (MPa) 172.9 178.5 Tensile strengthat break (MPa) 172.8 178.5 Elongation at break (%) 2.1 2.6 Tensilemodulus (MPa) 11408 10292 *as described in Encyclopedia of PolymerScience and Engineering, 2^(nd) edition, vol. 16, page 223, temperatures240; 260; 280; 290; 300.

As can be seen from the table, both formulations have good mechanicaland electrical properties with excellent flammability, but the productaccording to the present invention has better flow in the mold andhigher impact strength.

While embodiments of the invention have been described by way ofillustration, it will be understood that the invention may be carriedout with many modifications, variations and adaptations, withoutdeparting from its spirit or exceeding the scope of the claims.

1. A method for the preparation of a flame retardant (FR) forengineering thermoplastic compositions, said FR containing less than 100ppm of organic solvents with boiling point lower than 250° C. andincreasing melt flow index of said compositions while minimizingcorrosion of metallic parts being in contact with said compositions,said FR being a high molecular weight brominated expoxide (HMW BE)comprising a mixture of compounds of formula (I) and/or formula (II)and/or formula (III):

wherein n is an integer; and wherein at least 80 mol % of the end groupsof all three formulae in the mixture aretribromophenyl-oxo-2-hydroxypropyl groups, and at most 20 mol % of saidend groups are glycidyl groups; said FR being characterized by amolecular weight of between 7,000 and 50,000 Daltons; and a freetribromophenol content less than 0.1 wt %; wherein said method comprisesthe steps of: a) preparing low molecular weight brominated epoxide (LMWBE) having a molecular weight of between 650 and 3,500 Daltons, and acontent of organic solvents, with boiling point lower than 250° C.,lower than 100 ppm of said LMW BE; and b) reacting said LMW BE withtetrabromobisphenol-A (TBBA), and with a component selected from thegroup consisting of tribromophenol (TBP), tribromophenylglycidyl etherand a mixture thereof, in the presence of a catalyst, wherein saidreaction takes place without addition of any solvent, at a temperatureof from 100° C. to 250° C., said method being characterized in that itdoes not include any step of removing the solvent from said highmolecular weight brominated expoxide.
 2. A flame retardant (FR) forengineering thermoplastic compositions, said FR containing less than 100ppm of organic solvents with boiling point lower than 250° C. whileincreasing melt flow index of said compositions and minimizing corrosionof metallic parts being in contact with said compositions, preparedaccording to the method claim 1, which comprises a mixture of compoundsof formula (I) and/or formula (II) and/or formula (III):

wherein n is an integer; and wherein at least 80 mol % of the end groupsof all three formulae in the mixture aretribromophenyl-oxo-2-hydroxypropyl groups, and at most 20 mol % of saidend groups are glycidyl groups; said retardant being characterized by:i) a molecular weight of between 7,000 and 50,000 Daltons; ii) a freetribromophenol content less than 0.1 wt % of the whole flame retardant;and iii) a content of organic solvents, with boiling point lower than250° C., lower than 100 ppm of the whole flame retardant.
 3. A flameretardant according to claim 2, wherein 85 to 100 mol % of the endgroups are tribromophenyl-oxo-2-hydroxypropyl groups and 0 to 15 mol %of the end groups are glycidyl groups.
 4. A flame retardant according toclaim 2, wherein the content of said organic solvents with boiling pointlower than 250° C. is lower than 50 ppm.
 5. A flame retardant accordingto claim 2, comprising from 70 to 100 mol % of modified brominatedepoxides BEs of formula (II), from 30 to 0 mol % of partly modified BEsof formula (III), and from 10 to 0 mol % of unmodified BEs of formula(I).
 6. A flame retardant according to claim 2, having molecular weighthigher than 7,000 and lower than 30,000 Daltons.
 7. A flame retardantaccording to claim 2, having an acid number less than 1 mg KOH/g.
 8. Aflame retardant according to claim 7, having an acid number less than0.5 mg KOH/g.
 9. A flame retardant according to claim 2, having an epoxyequivalent of more than 10,000.
 10. A flame-retarded engineeringthermoplastic composition, comprising a base polymer selected from thegroup consisting of polyethylene terephthalate, of polybutyleneterephthalate, mixtures of polyethylene terephthalate with polybutyleneterephthalate, polyamides, and polycarbonate or its alloys, and furthercomprising at least one flame retardant according to claim
 2. 11. Aflame-retarded engineering thermoplastic composition according to claim10, further comprising hindered phenol antioxidants.
 12. Aflame-retarded engineering thermoplastic composition according to claim10, further comprising fillers and/or glass reinforcement and/orantioxidants and/or lubricants and/or pigments and/or anti-drippingagents and/or grades of talc that act as nucleating agents and thatreduce the injection molding cycle time.